The present invention relates to a thickness/depth measuring apparatus and method for accurate measurement of the depth of a film forming a mask and a groove or a workpiece during processing of the workpiece when forming the groove by a dry etching process so as to form a semiconductor device such as a storage device, an optical device such as a grating, or a magnetic device such as a magnetic head.
A depth measuring apparatus for measuring the depth of a groove is disclosed in Japanese Patent Application Laid-open No. 1-292202. This known depth measuring apparatus measures the depth of a pit on a stamping glass plate by irradiating the stamping glass plate with coherent light, detecting a plurality of reflected, diffracted light beams reflected by the surface of the stamping glass plate and calculating the ratio between the intensities of the reflected, diffracted light beams.
A thickness/depth measuring apparatus disclosed in Japanese Patent Application Laid-open No. 1-145504 measures the thickness of a film formed on a workpiece and the depth of a groove formed in the surface of the workpiece on the basis of the periods of variation of spectral intensities of regularly reflected light and scattered light obtained by irradiating the workpiece with light beams in a broad band and measuring the spectral intensities of the regularly reflected light and the scattered light.
The known depth measuring apparatus is able to measure the depth of a groove formed in the surface of a workpiece which is not provided with a processing mask of a resist film or the like, such as a stamping glass plate. However, the known depth measuring apparatus is in unable to measure the depth of the groove when the groove is formed on a workpiece coated with a resist film or the like, such as a workpiece for a semiconductor device or an optical device, due to the interferential effect of the resist film. Since the incident angle of the light beam in this known depth measuring apparatus is fixed, the depth measuring apparatus is unable to measure the depth of the groove with high accuracy even if the workpiece is not coated with a processing mask. That is, the known thickness/depth measuring apparatus is incapable of separately measuring the thickness of the film and the depth of the groove on the basis of the periods of variation of the spectral intensities because the respective periods of variation of the spectral intensities of the regularly reflected light and scattered light are approximately equal to each other when the optical path difference attributable to the thickness of the film and the optical difference attributable to the depth of the groove are approximately equal to each other.